海南岛抱板杂岩记录的多期构造热事件:锆石和独居石U-Pb年代学的制约

Polyphase tectonothermal events recorded in the Baoban complex from Hainan Island,South China:Constraint from zircon and monazite U-Pb geochronology

抱板杂岩(抱板群)是海南岛目前已发现的最古老前寒武纪结晶基底,记录了多期构造热事件,是研究海南岛大地构造属性的重要窗口。本文通过对海南岛冲卒岭地区抱板杂岩变质沉积岩、变质基性岩和伟晶岩脉的锆石和独居石LA-ICP-MS U-Pb年代学研究,来确定抱板杂岩所经历的多期构造热事件及其所代表的构造意义。研究结果显示,抱板杂岩主要由中元古代变质沉积岩、花岗质片麻岩和变质基性岩组成,经历了中元古代晚期-新元古代早期(1.3~0.9Ga)、早古生代(470~440Ma)、三叠纪(~230Ma)等多期构造热事件的改造。中元古代晚期-新元古代早期构造热事件与罗迪尼亚超大陆的汇聚有关;早古生代构造热事件与东冈瓦纳古陆北缘的增生造山作用有关;三叠纪构造热事件是印支陆块与华南陆块碰撞拼合的远程响应。综合上述研究成果和区域对比分析,认为海南岛与印支陆块具有相似的前寒武纪结晶基底和多期构造热事件的记录,表明二者具有明显的亲缘关系。

The Baoban complex,the oldest Precambrian crystalline basement in Hainan Island,recorded polyphase tectonothermal events,and provides a good window for studying the tectonic attribution of the Hainan Island.In this paper,zircon and monazite LA-ICP-MS U-Pb isotopic data of metasedimentary rocks,amphibolites and pegmatite dykes from the Baoban complex in the Chongzuling area of the southwestern part of Hainan Island are used to investigate the polyphase tectonothermal events in the Baoban complex and discuss their tectonic implications.The Mesoproterozoic metasedimentary rock,granitoids and amphibolite in the Baoban complex recorded three phases of tectonothermal events:Late Mesoproterozoic to Early Neoproterozoic event(1.3~0.9Ga),Early Paleozoic event(470~440Ma)and Triassic event(~230Ma).Late Mesoproterozoic to Early Neoproterozoic tectonothermal event was related to the formation of the Rodinia supercontinent.Early Paleozoic tectonothermal event can be linked to the accretionary orogenesis along the northern margin of East Gondwana.Triassic tectonothermal event is a remote response to the amalgamation of Indochina and South China blocks.Take into account of the above results and regional geology,it is inferred that the Hainan Island has similar Precambrian crystalline basement and polyphase tectonothermal histories with the Indochina block,indicating an obvious affinity between the two blocks.